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1. Field of the Invention
The present invention relates to a system for measuring the soil characteristics beneath the sea, and more particularly, in the placement of penetration devices to measure soil characteristics directly and to remove soil samples at the sea floor under deep water.
2. Description of the Related Technology
As land-based reserves of oil and natural gas have become more scarce or expensive to produce, oil companies have turned to offshore sources. Once precarious, offshore oil platform drilling is now commonplace and profitable. Consequently, oil companies have sought to extend the reach of offshore drilling into deeper water. Currently, the maximum depth for offshore rigs is roughly 8,000 feet, however more widespread deepwater drilling is desirable.
In order to secure platforms in deepwater, various techniques are used to secure anchors, such as continuous suction anchors, to the seafloor. Continuous suction anchors are relatively flat, hockey-puck shaped cylinders that are embedded into the seafloor. A suction pump is then attached to the anchor and water extracted from within the hollow caisson to generate a reaction against which a ship or floating platform may be attached. Unfortunately, continuous suction action is required in order to maintain the reaction as water seeps within the caisson from underneath the shallow walls of the caisson itself. This seepage varies with the type of soil in which the anchor is laid. Other types of anchors, namely plate anchors, also require information about the soil in which they are embedded. Consequently, in order to ensure proper anchoring, the soil of the anchor site must be tested. In some cases, the soil must be tested to a depth of 120 to 150 feet. In the prior art, the soil testing was accomplished by employing large ships, called drillships, to use drill pipe to reach the seafloor 8,000 or more feet below, so that the measuring cone could be implanted the additional 100 feet or more under the seafloor. Use of the large, expensive drillships, along with the crews and resources needed to construct the 5,000+feet of pipe needed, is very expensive and time consuming.
The alternatives to drillships in the prior art were large, heavy all-in-one apparatuses called a deadweight rig. The deadweight rig was lowered from a ship using a very heavyweight winch. As the name implies, the deadweight rig utilized a large dead weight, usually in the shape of a large hockey puck, that simply sat on the seafloor. The deadweight rig had its own internal hydraulic power system and associated control mechanism. The power and control for the deadweight rig, however, was supplied by the support ship through a large number of umbilical cords (called umbilicals). Unfortunately, the necessity for umbilicals has limited the utility of the deadweight rig, for the most part, to shallow water testing. Moreover the use of the deadweight, and the large amount of equipment for the rig carried on the deadweight, resulted in difficult and hazardous conditions on the support ship during deployment and recovery. Finally, all-in-one nature of the deadweight rig left little ability to cope with misfortune underwater.
There is, therefore, a need in the art for an apparatus and system for measuring seafloor soil characteristics without stringing 8,000 or more feet of drill pipe, without having to employ large ships with which to operate the drill tubing, and without the need to employ cumbersome deadweight seafloor templates.
The present invention solves the problems inherent in the prior art by providing an apparatus, system and method of measuring seafloor soil characteristics without requiring drill ships or thousands of feet of drill pipe.
The present invention is a deepwater suction caisson-based testing system. The present invention comprises a seabed unit, a support ship, and a remotely operated vehicle (xe2x80x9cROVxe2x80x9d). The seabed unit has a removable thrusting unit atop a capped suction caisson foundation. The suction caisson provides the required reaction force for a cone penetrometer that is co-axially driven by the thrusting unit. The thrusting unit contains all the active components of the system, which includes a rod thruster drive unit, ROV mateable quick disconnect ports, and visual gauges. The ROV is equipped with a stab for interfacing both with the pump of the suction caisson and with the thruster drive unit. The ROV is capable of mating and de-mating while underwater.
The present invention comprises four units, a seabed unit, a remotely operated vehicle (ROV), the cone rod measuring device, and a support ship. The seabed unit is lowered from the support ship by a wireline winch to the seafloor. A caisson on the seabed unit is used to secure the seabed unit to the seafloor. The ROV then inserts the cone rod measurement device into the upper thruster unit of the seabed unit. The thruster unit has a jacking mechanism for inserting the cone rod into the soil of the seafloor. The ROV supplies the hydraulic power and hydraulic controls to the hydraulic actuators of the thruster unit to control the manner and timing of the jacking process that inserts and extracts the cone rod measuring unit into the seafloor. The ROV is itself controlled remotely by operators stationed on the support ship. The ROV contains underwater cameras and control units that observe measurement gauges on the thruster unit and manipulate the hydraulic controls of the ROV and the thruster unit. The ROV can contain telemetry devices to extract and transmit data obtained from the cone rod measuring unit, or the cone rod measuring unit can contain its own electronic packages that store the information for downloading upon recovery by the support ship. Beside cone rod measuring units, the present invention can also employ coiled rod thrusting unit as well as a wide variety of other measuring devices.
The suction caisson includes the floor, guide cylinder, stab attachments, surface sling attachments, and valve ports. The suction caisson comprises a rolled and welded steel assembly that is capped at one end and open at the other. The guide cylinder extends forty-eight inches from the closed end of the suction caisson assembly into a cylindrical shell, forming a coaxial assembly. The caisson structural supports are constructed and arranged to facilitate structural integrity and embedment into the seafloor.
The present invention is equipped with a ROV interface (stab) receptacle to make connections from the ROV to the seabed unit. The stab receptacle is attached to a thruster unit supporting leg in case emergency removal of the thrusting unit from the caisson is needed. The ROV interface stab has suitable hydraulic and water connections to establish connection with the thrusting unit and the caisson.
A seawater pump is attached either to the caisson, to the ROV, or to the jacking unit. The seawater pump has variable pressure settings that are actuated by the ROV. Control of the clamp and rod thruster assemblies is through auxiliary solenoid valves. The ROV utilizes primary hydraulics for the caisson. The main pump/suction line of the caisson is equipped with a breakaway feature, which allows recovery of the upper assembly in the event of an emergency or failure in the caisson.
The ROV is equipped with a mating interface plate that is utilized for interfacing with the caisson mounted stab receptacle. The ROV mounted stab will decouple from the host ROV after mating and, through a suitable flexible hose, allowing the ROV to travel a minimum of 10 feet away from the caisson while remaining coupled. This procedure allows the ROV to move around the seabed unit and observe various gauges and the various devices on the seabed unit while being able to manipulate hydraulic controls.
Other and further objects, features and advantages will be apparent from the following description of presently preferred embodiments of the invention, given for the purpose of disclosure and taken in conjunction with the accompanying drawings.